Oxygen depletion in ponds
Ponds with warm water and overcrowded fish may be at risk for oxygen depletion. Hot, cloudy days, weeds, and low water levels all contribute to the problem.
Radio interview source: Billy Higginbotham, Wildlife & Fisheries Specialist, Texas Agrilife Extension Service
It's not uncommon for a pond to lose oxygen during hot, dry months. This can result in a fish kill.
Billy Higginbotham is a wildlife and fisheries specialist with Texas Agrilife Extension. He says warm water holds less oxygen than cold water, so that can trigger oxygen depletion. Combine this with hot, still cloudy days and the fish may be in trouble.
"The sunlight's blocked from the pond's surface," he says. "There's no photosynthetic activity going on where the plant life in the water can produce oxygen. If you have several days of a heavy cloud cover in a row, the oxygen production's being limited. And again with the increased water temperatures, the stage is somewhat set for an oxygen depletion to occur."
Higginbotham says weed control can also contribute to the problem. If the pond owner removes too many weeds, this reduces the oxygen levels.
In cases where the water levels are low, fish become crowded and fight for oxygen. You'll know the fish are in trouble when they're at the surface, gulping for air. If you suspect conditions are right for oxygen depletion, Higginbotham recommends assessing your pond at daylight.
"In a 24-hour period, oxygen will typically be at its dead-level lowest right at daylight," says Higginbotham. "Then as the sun comes up, the opportunity for photosynthesis to occur kicks in and oxygen levels can increase, so go down and check early in the morning. If you do see those fish up, you've got a short period of time to react. And typically, there's a couple of things a pond owner can do."
One is to back a boat on a trailer down into the water. Crank the motor, put it in gear, and let it circulate the pond water. The other is if you have access to a pump, set the intake near the surface. The water will be aerated as it shoots back out.
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